Transparent electro-conductive structure, process for its production, transparent electro-conductive layer forming coating fluid used for its production, and process for preparing the coating fluid

ABSTRACT

A transparent electro-conductive structure comprising a transparent substrate and formed successively thereon a transparent electro-conductive layer and a transparent coat layer, which is used, e.g., front panels of display device such as CRTs. The transparent electro-conductive layer is composed chiefly of i) noble-metal-coated fine silver particles having an average particle diameter of from 1 nm to 100 nm, the fine silver particles being surface-coated with gold or platinum alone or a composite of gold and platinum, and ii) a binder matrix. A transparent electro-conductive layer forming coating fluid used in the production of this transparent conductive structure comprises a solvent and noble-metal-coated fine silver particles dispersed in the solvent and having an average particle diameter of from 1 nm to 100 nm, the fine silver particles being surface-coated with gold or platinum alone or a composite of gold and platinum.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a transparent electro-conductive structurehaving a transparent substrate and formed successively thereon atransparent electro-conductive layer and a transparent coat layer, whichis used in, e.g., front panels of display devices such as CRTs. Moreparticularly, this invention relates to a transparent electro-conductivestructure having superior weatherability, conductivity and so forth andalso achievable of cost reduction in manufacture, and a process for itsproduction, and also relates to a transparent electro-conductive layerforming coating fluid used for its production, and a process forpreparing such a coating fluid.

2. Description of the Related Art

With office automation made in recent years, a variety of officeinformation instruments have been introduced into offices, and in anoffice environment it is no longer uncommon to do office work all daywhile facing display devices of office information instruments.

Now, in office work done sitting close to cathode ray tubes (CRTs) ofcomputers, as an example of the office information instruments, it isrequired for the display screens to be easy to watch and not to causevisual fatigue, as well as to be free from attraction of dust andelectric shock which are due to the electrostatic charging on the CRTsurfaces. Moreover, in addition to these, any adverse influence on humanbodies by low-frequency electromagnetic waves generated from CRTs hasbeen recently a concern, and it is desired for such electromagneticwaves not to leak outside.

The electromagnetic waves are generated from deflecting coils andflyback transformers and a large quantity of electromagnetic wavesincreasingly tend to leak to surroundings as CRTs become larger in size.

Now, the leakage of magnetic fields can be prevented to a great extentby designing, e.g., by the changing of deflecting coils in terms ofshape. As for the leakage of electric fields, it can be prevented byforming a transparent electro-conductive layer on the front-glasssurface of a CRT.

Measures to prevent such leakage of electric fields are theoreticallythe same as the countermeasures taken in recent years to preventelectrostatic charging. However, the transparent electro-conductivelayer is required to have a much higher conductivity than any conductivelayers formed for preventing the electrostatic charging. Morespecifically, a layer with a surface resistance of about 10⁸ ohm persquare is considered sufficient for the purpose of preventingelectrostatic charging. However, in order to prevent the leakage ofelectric fields (i.e., electric-field shielding), it is necessary toform at least a transparent electro-conductive layer with a lowresistance of 10⁶ ohm per square or below, and preferably 10³ ohm persquare or below.

Under such circumstances, as countermeasures for such a necessity, someproposals have been made. In particular, as a method that can attain alow surface resistance at a low cost, a method is known in which atransparent electro-conductive layer forming coating fluid prepared bydispersing conductive fine particles in a solvent together with aninorganic binder such as an alkyl-silicate, is coated on a front glassfor a CRT, followed by drying and then baking at a temperature of 200°C. or below.

This method making use of such a transparent electro-conductive layerforming coating fluid is much simpler than any other transparentelectro-conductive layer forming method employing vacuum evaporation(vacuum deposition), sputtering or the like, and can enjoy a lowproduction cost. Thus, it is a very advantageous method forelectric-field shielding that can be applied to CRTs.

As the transparent electro-conductive layer forming coating fluid usedin this method, a coating fluid is known in which indium tin oxide (ITO)is used as the conductive fine particles. Since, however, the resultantfilm has a surface resistance of as high as 10⁴ to 10⁶ ohm per square, acorrective circuit for cancelling electric fields is required in orderto sufficiently shield the leaking electric fields. Hence, there hasbeen a problem of a production cost which is correspondingly ratherhigh. Meanwhile, in the case of a transparent electro-conductive layerforming coating fluid making use of a metal powder as the conductivefine particles, the resultant film may have a little lower transmittancethan in the case of the coating fluid making use of ITO, but alow-resistance film of from 10² to 10³ ohm per square can be formed.Accordingly, such a coating fluid, which makes the corrective circuitunnecessary, is advantageous in cost and is considered to becomeprevailing in future.

Fine metal particles used in the above transparent electro-conductivelayer forming coating fluid, as disclosed in Japanese Patent Laid-openApplication No. 8-77832 and No. 9-55175, are limited to noble metalssuch as silver, gold, platinum, rhodium and palladium, which may hardlybe oxidized in air. This is because, if fine particles of a metal otherthan noble metals as exemplified by iron, nickel or cobalt are used,oxide films are necessarily formed on the surfaces of such fine metalparticles in the atmosphere, making it impossible to attain a goodconductivity in the transparent electro-conductive layer.

From another aspect, in order to make display screens easy to watch, ananti-glare treatment is conducted on the surfaces of face panels so thatthe screens can be restrained from reflecting light. This anti-glaretreatment can be made by a method in which a finely rough surface isprovided to make a diffused reflection on the surface greater. Thismethod, however, can not be said to be preferable because its employmentmay bring about a low resolution, resulting in a low picture quality.Accordingly, it is preferable to make the anti-glare treatment by aninterference method in which the refractive index and layer thickness ofa transparent film are controlled so that the reflected light mayinterfere destructively with the incident light. In order to attain theeffect of low reflection by such an interference method, it is common toemploy a film of double-layer structure formed of ahigh-refractive-index film and a low-refractive-index film each havingan optical layer thickness set at ¼λ and ¼λ, or ½λ and ¼λ, respectively(λ: wavelength). The film formed of fine particles of indium tin oxide(ITO) as mentioned above is also used as a high-refractive-index film ofthis type.

In metals, among parameters constituting an optical constant n-ik (n:refractive index; i²=−1; k: extinction coefficient), the value of n issmall but the value of k is extremely greater than that in ITO, andhence, also when the transparent electro-conductive layer formed of finemetal particles is used, the effect of low reflection that isattributable to the interference of light can be attained by thedouble-layer structure as in the case of ITO (a high-refractive-indexfilm).

Now, as stated above, fine metal particles used in the conventionaltransparent electro-conductive layer forming coating fluid are limitedto noble metals such as silver, gold, platinum, rhodium and palladium.To compare electrical resistance of these, platinum, rhodium andpalladium have a resistivity of 10.6, 5.1 and 10.8 μΩ·cm, respectively,which are higher than 1.62 and 2.2 μΩ·cm of silver and gold,respectively. Hence, it has been advantageous to use fine silverparticles or fine gold particles in order to form a transparentelectro-conductive layer having a low surface resistance.

The use of fine silver particles, however, may cause a greatdeterioration due to sulfidation or contact with brine to cause aproblem of weatherability. On the other hand, the use of fine goldparticles can eliminate the problem on weatherability, but has had aproblem on cost as in the case when fine platinum particles, finerhodium particles or fine palladium particles are used. Moreover, theuse of fine gold particles also has a problem that, because thetransparent electro-conductive layer formed absorbs a part of visiblelight rays in itself because of the optical properties inherent in gold,the film can not be used in the display surfaces of display devices suchas CRTs where flat transmitted-light profiles are required over thewhole region of visible light rays.

SUMMARY OF THE INVENTION

The present invention was made taking note of such problems.Accordingly, an object of the present invention is to provide atransparent electro-conductive structure having superior weatherability,conductivity and so forth and also achievable of cost reduction inmanufacture.

Another object of the present invention is to provide a process forproducing a transparent electro-conductive structure having superiorweatherability, conductivity and so forth.

Still another object of the present invention is to provide atransparent electro-conductive layer forming coating fluid used in theproduction of a transparent electro-conductive structure having superiorweatherability, conductivity and so forth.

A further object of the present invention is to provide a process forpreparing the transparent electro-conductive layer forming coatingfluid.

More specifically, in the present invention, the transparentelectro-conductive structure comprises a transparent substrate andformed successively thereon a transparent electro-conductive layer and atransparent coat layer, wherein;

the transparent electro-conductive layer is composed. chiefly of i)noble-metal-coated fine silver particles having an average particlediameter of from 1 nm to 100 nm, the fine silver particles beingsurface-coated with gold or platinum alone or a composite of gold andplatinum, and ii) a binder matrix.

The process for producing this transparent electro-conductive structurecomprises;

coating on a transparent substrate a transparent electro-conductivelayer forming coating fluid comprising a solvent and noble-metal-coatedfine silver particles dispersed in the solvent and having an averageparticle diameter of from 1 nm to 100 nm, the fine silver particlesbeing surface-coated with gold or platinum alone or a composite of goldand platinum; and

coating a transparent coat layer forming coating fluid on thetransparent electro-conductive layer thus formed, followed by heating.

The transparent electro-conductive layer forming coating fluid used inthe production of the transparent electro-conductive structure comprisesa solvent and noble-metal-coated fine silver particles dispersed in thesolvent and having an average particle diameter of from 1 nm to 100 nm,the fine silver particles being surface-coated with gold or platinumalone or a composite of gold and platinum.

The process for preparing the transparent electro-conductive layerforming coating fluid comprises;

a noble-metal-coated fine silver particle making step of adding to acolloidal dispersion of fine silver particles i) a reducing agent and atleast one of an alkali metal aurate solution and an alkali metalplatinate solution or ii) a reducing agent and a solution of mixture ofan alkali metal aurate and an alkali metal platinate, to coat gold orplatinum alone or a composite of gold and platinum on the surfaces ofthe fine silver particles to obtain a colloidal dispersion ofnoble-metal-coated fine silver particles;

a desalting and concentrating step of subjecting the colloidaldispersion of noble-metal-coated fine silver particles to desaltingtreatment to lower its electrolyte concentration and to concentratingtreatment to concentrate the colloidal dispersion, to obtain aconcentrated dispersion of noble-metal-coated fine silver particles; and

a solvent mixing step of adding to the concentrated dispersion ofnoble-metal-coated fine silver particles a solvent alone or a solventcontaining at least one of conductive fine oxide particles and aninorganic binder, to obtain the transparent electro-conductive layerforming coating fluid.

Another process for preparing the transparent electro-conductive layerforming coating fluid comprises;

a noble-metal-coated fine silver particle making step of adding to acolloidal dispersion of fine silver particles i) at least one of analkali metal aurate solution and an alkali metal platinate solution orii) a solution of mixture of an alkali metal aurate and an alkali metalplatinate, to coat gold or platinum alone or a composite of gold andplatinum on the surfaces of the fine silver particles by the aid ofdisplacement reaction caused by a difference in ionization tendencybetween silver, gold and platinum, to obtain a colloidal dispersion ofnoble-metal-coated fine silver particles;

a desalting and concentrating step of subjecting the colloidaldispersion of noble-metal-coated fine silver particles to desaltingtreatment to lower its electrolyte concentration and to concentratingtreatment to concentrate the colloidal dispersion, to obtain aconcentrated dispersion of noble-metal-coated fine silver particles; and

a solvent mixing step of adding to the concentrated dispersion ofnoble-metal-coated fine silver particles a solvent alone or a solventcontaining at least one of conductive fine oxide particles and aninorganic binder, to obtain the transparent electro-conductive layerforming coating fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical representation showing reflection profiles oftransparent electro-conductive structures according to Example 1 andComparative Examples 1 and 2.

FIG. 2 is a graphical representation showing transmission profiles oftransparent electro-conductive structures according to Example 1 andComparative Example 1.

FIG. 3 is a graphical representation showing a reflection profile of atransparent electro-conductive structure according to Example 1.

FIG. 4 is a graphical representation showing transmission profiles ofthe transparent electro-conductive structure according to Example 1 anda glass substrate which is a constituent member of this structure.

FIG. 5 is a graphical representation showing a reflection profile of atransparent electro-conductive structure according to Example 2.

FIG. 6 is a graphical representation showing transmission profiles ofthe transparent electro-conductive structure according to Example 2 anda glass substrate which is a constituent member of this structure.

FIG. 7 is a graphical representation showing a reflection profile of atransparent electro-conductive structure according to Example 5.

FIG. 8 is a graphical representation showing transmission profiles ofthe transparent electro-conductive structure according to Example 5 anda glass substrate which is a constituent member of this structure.

FIG. 9 is a graphical representation showing a reflection profile of atransparent electro-conductive structure according to Example 6.

FIG. 10 is a graphical representation showing transmission profiles ofthe transparent electro-conductive structure according to Example 6 anda glass substrate which is a constituent member of this structure.

FIG. 11 is a graphical representation showing reflection profiles oftransparent electro-conductive structures according to Example 8 andComparative Examples 1 and 2.

FIG. 12 is a graphical representation showing transmission profiles oftransparent electro-conductive structures according to Example 8 andComparative Example 1.

FIG. 13 is a graphical representation showing a reflection profile of atransparent electro-conductive structure according to Example 8.

FIG. 14 is a graphical representation showing transmission profiles ofthe transparent electro-conductive structure according to Example 8 anda glass substrate which is a constituent member of this structure.

FIG. 15 is a graphical representation showing a reflection profile of atransparent electro-conductive structure according to Example 9.

FIG. 16 is a graphical representation showing transmission profiles ofthe transparent electro-conductive structure according to Example 9 anda glass substrate which is a constituent member of this structure.

FIG. 17 is a graphical representation showing a reflection profile of atransparent electro-conductive structure according to Example 11.

FIG. 18 is a graphical representation showing transmission profiles ofthe transparent electro-conductive structure according to Example 11 anda glass substrate which is a constituent member of this structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described below in detail.

First the present invention is based on the standpoint that gold orplatinum is chemically stable and has excellent weatherability, chemicalresistance, oxidation resistance and so forth and hence fine silverparticles can be improved in chemical stability by coating gold orplatinum alone or a composite of gold and platinum on their surfaces. Aspreviously stated, platinum has a slightly higher electrical resistancethan silver and gold. However, the gold or platinum alone or thecomposite of gold and platinum is used as coating layers on the surfacesof fine silver particles and hence it by no means damages the goodconductivity of the silver. Incidentally, in place of the coating of thefine silver particles with the gold or platinum alone or composite ofgold and platinum, one may contemplate making silver into an alloy withgold or platinum or with gold and platinum to form fine alloy particles.Such a method, however, makes it necessary to use the gold or platinumalone or the gold and platinum in a high concentration in the whole fineparticles, and hence requires the gold or platinum or the gold andplatinum in a large quantity, creating a difficulty in view of cost.From the foregoing standpoint, in the present invention,noble-metal-coated fine silver particles obtained by coating the gold orplatinum alone or composite of gold and platinum on the surfaces of finesilver particles are used so that the above problems can be solved.

More specifically, the present invention is a transparentelectro-conductive structure having a transparent substrate and formedsuccessively thereon a transparent electro-conductive layer and atransparent coat layer, characterized in that the transparentelectro-conductive layer is composed chiefly of i) noble-metal-coatedfine silver particles having an average particle diameter of from 1 nmto 100 nm, the fine silver particles being surface-coated with gold orplatinum alone or a composite of gold and platinum, and ii) a bindermatrix.

The coating of the gold or platinum alone or composite of gold andplatinum on the surfaces of fine silver particles constituting thetransparent electro-conductive layer brings about a great improvement inweatherability, chemical resistance and so forth because the silver inthe interior of the noble-metal-coated fine silver particles isprotected by the gold or platinum alone or composite of gold andplatinum.

For example, when a transparent electro-conductive layer comprised offine silver particles and a binder matrix composed chiefly of siliconoxide is immersed in 5% brine, chlorine ions in the brine react with thefine silver particles of the transparent electro-conductive layer tocause great deterioration in a short time of 1 hour or less and evencause film peeling in the transparent electro-conductive layer. However,in the case of the transparent electro-conductive layer in which thenoble-metal-coated fine silver particles coated with the gold orplatinum alone or a composite of gold and platinum are used, thetransparent electro-conductive layer is not changed at all even whenimmersed for 24 hours or longer, depending on the coating weight of thegold or platinum alone or composite of gold and platinum, and showssuperior weatherability. Also, gold and platinum do not oxidize in theatmosphere, and hence do not cause any deterioration of electricalresistance due to oxidation. Thus, the transparent electro-conductivelayer in which the noble-metal-coated fine silver particles are used hasbetter surface resistance than the transparent electro-conductive layerin which conventional fine silver particles are used .

Here, the noble-metal-coated fine silver particles are required to havean average particle diameter of from 1 nm to 100 nm. Noble-metal-coatedfine silver particles having an average particle diameter smaller than 1nm can be produced with difficulty, and also tend to aggregate, thussuch particles are not practical. As for those larger than 100 nm, thetransparent electro-conductive layer may have too low a transmittance ofvisible light rays, and, even if formed in a small layer thickness toensure a high transmittance of visible light rays, the layer may havetoo high a surface resistance, thus such particles are not practical.Incidentally, the average particle diameter herein used refers toaverage particle diameter of fine particles observed on a transmissionelectron microscope (TEM).

In the noble-metal-coated fine silver particles, the gold or platinumalone or composite of gold and platinum may be in a coating weight setwithin the range of from 5 to 100 parts by weight, and preferably from10 to 50 parts by weight, based on 100 parts by weight of silver. If thegold or platinum alone or composite of gold and platinum is in a coatingweight less than 5 parts by weight, the protection attributable tocoating may be less effective to make the weatherability poorer. If onthe other hand, it is in a coating weight more than 100 parts by weight,a difficulty may occur in view of cost.

For the purpose of improving film transmittance in the transparentelectro-conductive layer, conductive fine oxide particles of at leastone selected from tin oxide, antimony tin oxide and indium tin oxide mayalso be added to the interior of the transparent electro-conductivelayer. In this instance, the noble-metal-coated fine silver particlesand conductive fine oxide particles in the transparentelectro-conductive layer may be in a mixing ratio set so that theconductive fine oxide particles are in an amount within the range offrom 1 to 200 parts by weight, and preferably from 10 to 100 parts byweight, based on 100 parts by weight of the noble-metal-coated finesilver particles. If the conductive fine oxide particles are mixed in anamount less than 1 part by weight, the addition of the conductive fineoxide particles cannot be effective, and if on the other hand they aremixed in an amount more than 200 parts by weight, the transparentelectro-conductive layer may have too high a resistance to be practical.As in the case of the noble-metal-coated fine silver particles, theconductive fine oxide particles may preferably have an average particlediameter of from about 1 nm to about 100 nm.

The transparent electro-conductive layer forming coating fluid used toform the transparent electro-conductive layer can be prepared by aprocess as described below.

First, a colloidal dispersion of fine silver particles is made up by aknown process [e.g., the Carey-Lea process, Am. J. Sci., 37, 47 (1889),Am. J. Sci., 38 (1889)]. More specifically, a mixed solution of anaqueous iron (II) sulfate solution and an aqueous sodium citratesolution are added to an aqueous silver nitrate solution to carry out areaction, and the resultant sediment is filtered and washed, followed byaddition of pure water, whereby a colloidal dispersion of fine silverparticles (Ag: 0.1 to 10% by weight) can be made simply. This colloidaldispersion of fine silver particles may be made up by any method so longas fine silver particles having an average particle diameter of from 1nm to 100 nm can be dispersed, without any limitation to the abovemethod. To the colloidal dispersion of fine silver particles thusobtained, a reducing agent is added and an alkali metal aurate solutionor an alkali metal platinate solution is further added thereto, or analkali metal aurate solution and an alkali metal platinate solution areadded separately, or a solution of mixture of an alkali metal aurate andan alkali metal platinate is added, to thereby coat gold or platinumalone or a composite of gold and platinum on the surfaces of the finesilver particles. Thus, a colloidal dispersion of noble-metal-coatedfine silver particles can be obtained.

In this step of making noble-metal-coated fine silver particles, adispersant may optionally be added in a small quantity to any one of, orall of, the colloidal dispersion of fine silver particles, the alkalimetal aurate solution, the alkali metal platinate solution and thesolution of mixture of an alkali metal aurate and an alkali metalplatinate.

Here, in the above step of making noble-metal-coated fine silverparticles, the reaction to coat the gold or platinum alone or compositeof gold and platinum on the surfaces of fine silver particles takesplace because minute and fine silver particles are already present in alarge quantity in the solution at the time when gold or platinum isproduced as a result of the reduction of an aurate or a platinate, andbecause the coating proceeds under conditions more advantageous in viewof energy when gold or platinum grows on the surfaces of fine silverparticles serving as nuclei than when gold or platinum makes nucleation(homogeneous nucleation) by itself. Thus, the presence of minute andfine silver particles in a large quantity in the solution is aprerequisite at the time when gold or platinum is produced as a resultof the reduction of an aurate or a platinate, and hence the timing atwhich the aurate solution or platinate solution, the aurate solution andplatinate solution or the solution of mixture of the aurate andplatinate and the reducing agent are added in the colloidal dispersionof fine silver particles in the step of making noble-metal-coated finesilver particles may preferably be so controlled that the reducing agentis added at least prior to adding the aurate solution or platinatesolution, the aurate solution and platinate solution or the solution ofmixture of an alkali metal aurate and an alkali metal platinate. Morespecifically, this is because, in the case when the reducing agent andthe aurate solution or platinate solution, or the reducing agent and theaurate solution and platinate solution, or the reducing agent and thesolution of mixture of the aurate and platinate are added in thecolloidal dispersion of fine silver particles in the state they aremixed, the gold or platinum may be produced as a result of the reductionof the aurate or platinate and also the gold or platinum may makenucleation (homogeneous nucleation) by itself, at the stage where theaurate solution or platinate solution, the aurate solution and platinatesolution or the solution of mixture of the aurate and platinate is mixedin the reducing agent, so that the reaction to coat the gold or platinumalone or composite of gold and platinum on the surfaces of fine silverparticles may not take place even when the aurate solution and/orplatinate solution or the like and the reducing agent are added to thecolloidal dispersion of fine silver particles after they are mixed.

As the reducing agent, hydrazine N₂H₄, borohydrates such as sodiumborohydrate NaBH₄, and formaldehyde may be used, but without limitationto these. Any reducing agents may be used so long as they do not causeaggregation of ultrafine silver particles when added in the colloidaldispersion of fine silver particles and can reduce the aurate andplatinate to gold and platinum, respectively.

For example, the reduction reaction taking place when potassium aurateKAu(OH)₄ and potassium platinate K₂Pt(OH)₆ are each reduced withhydrazine or sodium borohydrate is represented by the following scheme.

KAU(OH)₄+3/4N₂H₄→Au+KOH+3H₂O+3/4N₂↑

 K₂PT(OH)₆+N₂H₄→Pt+2KOH+4H₂O+N₂↑

KAU(OH)₄+3/4NaBH₄→Au+KOH+3/4NaOH+3/4H₃BO₃+3/2H₂↑

K₂Pt(O )₆+NaB₄→Pt+2KOH+NaOH+H_(3/4)BO₃+2H₂↑

Here, when sodium borohydrate is used as the reducing agent, theelectrolyte is produced by reduction reaction in a high concentration ascan be confirmed by the above reaction scheme, and hence the fineparticles tend to aggregate as will be described later. Thus, there is alimit on its quantity when added as the reducing agent, and there is adisadvantage that a high silver concentration cannot be achieved in thecolloidal dispersion of fine silver particles used.

On the other hand, when hydrazine is used as the reducing agent, lesselectrolyte is produced as can be confirmed by the above reactionscheme, thus the hydrazine is more suited as the reducing agent.

Incidentally, if any salts other than the alkali metal aurate and alkalimetal platinate as exemplified by chloroauric acid HAuCl₄ andchloroplatinic acid H₂PtCl₆, or chloroaurates such as NaAuCl₄ and KAuCl₄and chloroplatinates such as Na₂PtCl₆ and K₂PtCl₆ are used as materialsfor coating gold and platinum, the reduction reaction caused byhydrazine is represented by the following scheme.

XAuCl₄+3/4N₂H₄→Au+XCl+3HCl+3/4N₂↑

X₂ PtCl₆+N₂H₄→Pt+2XCl+4HCl+N₂↑(X: H, Na or K)

When chloroauric acid and the like are used in this way, not only is theelectrolyte produced by the reduction reaction in a high concentration,but also chlorine ions are produced, and hence react with the finesilver particles to form silver chloride, which is slightly soluble.Thus, it is difficult to use these as materials for forming thetransparent electro-conductive layer according to the present invention.

In the above process, it is also possible not to use hydrazine and tocoat the gold or platinum alone or composite of gold and platinum by theaid of displacement reaction caused by a difference in ionizationtendency between silver, gold and platinum.

More specifically, the alkali metal aurate solution or alkali metalplatinate solution or the alkali metal aurate solution and alkali metalplatinate solution or the solution of mixture of an alkali metal aurateand an alkali metal platinate may be added directly to the colloidaldispersion of fine silver particles, whereby the colloidal dispersion ofnoble-metal-coated fine silver particles can be obtained.

Incidentally, the reaction to coat gold or platinum is represented bythe following scheme.

3Ag+Au³⁺→3Ag⁺+Au

4Ag+Pt⁴⁺→4Ag⁺+Pt

The colloidal dispersion of noble-metal-coated fine silver particlesthus obtained may thereafter preferably be subjected to desalting bydialysis, electrodialysis, ion exchange, ultrafiltration or the like tolower the concentration of the electrolyte in the dispersion. This isbecause colloids may commonly aggregate when electrolytes are in a highconcentration. This phenomenon is known also as the Schultz-Hardy'srule. For the same reasons, in the case when the conductive fine oxideparticles of one selected from tin oxide, antimony tin oxide and indiumtin oxide are mixed in the colloidal dispersion of noble-metal-coatedfine silver particles or the transparent electro-conductive layerforming coating fluid, such conductive fine oxide particles or adispersion thereof may also preferably be desalted thoroughlybeforehand.

Next, the colloidal dispersion of noble-metal-coated fine silverparticles which has been subjected to desalting treatment isconcentrated to obtain a concentrated dispersion of noble-metal-coatedfine silver particles. Then, to this concentrated dispersion ofnoble-metal-coated fine silver particles, an organic solvent alone or anorganic solvent containing at least one of conductive fine oxideparticles and an inorganic binder is added to make component adjustment(e.g., fine-particle concentration, water concentration). Thus, thetransparent electro-conductive layer forming coating fluid is obtained.

When ultrafiltration is employed as a desalting method, thisultrafiltration also acts as a concentrating treatment as will bedescribed later, and hence it is also possible to carry out thedesalting treatment and the concentrating treatment simultaneously.Accordingly, with regard to the desalting treatment and concentratingtreatment of the colloidal dispersion in which the noble-metal-coatedfine silver particles stand dispersed, their order may be set as desireddepending on the manner of treatment to be employed. The desaltingtreatment and concentrating treatment may be made simultaneously whenultrafiltration or the like is employed.

In the present invention, the fact that the gold or platinum alone orcomposite of gold and platinum is coated on the surfaces of fine silverparticles is founded by technical confirmation made by observation ofparticles on a transmission electron microscope (TEM) and analysis ofcomponents (EDX: energy dispersive X-ray analyzer), being made since anychanges in particle diameter are little seen before and after thecoating of the gold or platinum alone or composite of gold and platinumand that the gold or platinum alone or composite of gold and platinum isdistributed uniformly on each particle, and also coordination number(the number of coordination) of the gold or platinum alone or compositeof gold and platinum, examined by EXAFS (extended X-ray absorption finestructure) analysis.

With regard to the form in which the composite of gold and platinumcovers the fine silver particles, various forms are possible dependingon differences coming from whether the aurate solution and the platinatesolution are used or the solution of mixture of the aurate and platinatein the step of coating the composite of gold and platinum (i.e., thenoble-metal-coated fine silver particle making step) or depending ondifferences in the timing of mixing these solutions and in theconcentration of the aurate and platinate. More specifically, dependingon the differences in these conditions, various forms are possible suchthat the gold covers the fine silver particles on their whole surfacesor in part and the platinum further covers them on the whole surfaces,or conversely the platinum covers the fine silver particles on the wholesurfaces or in part and the gold further covers them on the wholesurfaces, or the platinum and gold standing each alone withoutoverlapping each other, or in the form of an alloy, cover the finesilver particles on their whole surfaces.

The treatment to concentrate the colloidal dispersion ofnoble-metal-coated fine silver particles can be made by any ofconventional methods such as reduced pressure evaporation andultrafiltration. Also, the transparent electro-conductive layer formingcoating fluid may preferably have a water concentration of from 1 to 20%by weight. If it has a water concentration of more than 20% by weight,in some cases the transparent electro-conductive layer forming coatingfluid tends to cause cissing due to a high surface tension of water inthe course of drying after it has been coated on the transparentsubstrate.

The problem of cissing can be solved by adding a surface-active agent inthe transparent electro-conductive layer forming coating fluid. However,there may arise another problem that the mixing of the surface-activeagent tends to cause faulty coating. Thus, it is preferable for thetransparent electro-conductive layer forming coating fluid to have awater concentration of from 1 to 20% by weight.

There are no particular limitations on the above organic solvent, whichmay appropriately selected depending on coating methods and film-formingconditions. It may include, but not limited to, e.g., alcohol typesolvents such as methanol, ethanol, isopropanol, butanol, benzyl alcoholand diacetone alcohol, ketone type solvents such as acetone, methylethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclohexanone andisophorone, glycol derivatives such as propylene glycol methyl ether andpropylene glycol ethyl ether, dimethylformamide (DMF), andN-methyl-2-pyrrolidone (NMP).

Using the transparent electro-conductive layer forming coating fluidthus obtained, the transparent electro-conductive structure can beobtained which has the transparent substrate and formed thereon thetransparent electro-conductive layer composed chiefly of i)noble-metal-coated fine silver particles having an average particlediameter of from 1 nm to 100 nm and ii) a binder matrix and atransparent coat layer further formed thereon.

A transparent double-layer film constituted of the transparentelectro-conductive layer and the transparent coat layer can be formed onthe transparent substrate by a method described below. That is, thetransparent electro-conductive layer forming coating fluid composedchiefly of the solvent and the noble-metal-coated fine silver particleshaving an average particle diameter of from 1 nm to 100 nm is coated onthe transparent substrate, such as a glass substrate or a plasticsubstrate, by a coating process such as spray coating, spin coating,wire bar coating or doctor blade coating, optionally followed by drying.Thereafter, a transparent coat layer forming coating fluid composedchiefly of, e.g. silica sol is over-coated (top-coated) by the samecoating process as the above.

Next, after the overcoating, the coating formed is heated at atemperature of about, e.g., 50 to 250° C. to cause the over-coatedtransparent coat layer to harden, thus the transparent double-layerfilms are formed. Incidentally, the heating at a temperature of about 50to 250° C. may cause no problem because the noble-metal-coated finesilver particles are protected by the gold or platinum alone orcomposite of gold and platinum. If, however, conventional fine silverparticles are used, the surface resistance may increase at a temperaturehigher than 200° C. as a result of oxidative diffusion to causedeterioration of films.

Here, when the transparent coat layer forming coating fluid composedchiefly of silica sol or the like is over-coated by the above coatingprocess, the silica sol thus over-coated (this silica sol turns into abinder matrix composed chiefly of silicon oxide as a result of theheating) soaks into gaps between noble-metal-coated fine silverparticles present in the layer formed by the transparentelectro-conductive layer forming coating fluid previously coated,composed chiefly of the solvent and the noble-metal-coated fine silverparticles. Thus, an improvement in conductivity, an improvement instrength and a more improvement in weatherability can be achievedsimultaneously.

Moreover, the transparent double-layer film structure constituted of thetransparent electro-conductive layer and the transparent coating layercan make the reflectance of the transparent double-layer film greatlylow, because the transparent electro-conductive layer comprising thenoble-metal-coated fine silver particles dispersed in the binder matrixcomposed chiefly of silicon oxide has, in its optical constant (n-ik), arefractive index n which is not so great but has a great extinctioncoefficient. Then, as shown in FIG. 1, in comparison with instanceswhere fine ITO particles (Comparative Example 2) or fine silverparticles (Comparative Example 1) are used, the reflectance is improvedat a short wavelength region (380 to 500 nm) of visible light rays whennoble-metal-coated fine silver particles coated with gold alone(Example 1) are used. Also, the profile of transmitted light of thetransparent double-layer film is, as shown in FIG. 2, also improved atthe short wavelength region of visible light rays by coating gold aloneon the fine silver particles. For example, in comparison of standarddeviation in respect of the transmittance of only a transparentdouble-layer film, excluding the transparent substrate, at eachwavelength plotted at intervals of 5 nm of a wavelength region (380 to780 nm) of visible light rays, the standard deviation is about 7% whenfine silver particles (Comparative Example 1) are used, whereas it is asmall value of about 2 to 3% when the noble metal is coated (Examples 1to 11) on the fine silver particles, where very flat transmissionprofiles are obtained. The reason why the reflection and transmissioncharacteristics of these transparent double-layer films are improved isstill unclear, and is presumed to be a change in surface plasmon of finemetal particles that is attributable to the coating of the gold orplatinum alone or composite of gold and platinum on the fine silverparticles.

Here, as the silica sol, usable are a polymeric product obtained byadding water and an acid catalyst to an orthoalkyl-silicate to effecthydrolysis followed by dehydration condensation polymerization, or apolymeric product obtained by subjecting a commercially availablealkyl-silicate solution having already been subjected to hydrolysis andcondensation polymerization to proceed up to a 4- to 5-mer (tetramerfurther to pentamer), to hydrolysis and dehydration condensationpolymerization. Since the solution viscosity increases with progress ofdehydration condensation polymerization to finally make the productsolidify, the degree of dehydration condensation polymerization may beso controlled as to be not higher than the maximum viscosity at whichthe coating fluid can be coated on the transparent substrate such as aglass substrate or a plastic substrate. The degree of dehydrationcondensation polymerization is not particularly specified so long as itis kept at a level not higher than the maximum viscosity, but maypreferably be from about 500 to about 3,000 as weight-average molecularweight, taking account of film strength and weatherability. Then, thedehydration condensation polymerization is substantially completed atthe time the transparent double-layer film is heated and baked, and thealkyl-silicate partially hydrolyzed polymeric product turns into a hardsilicate film (a film composed chiefly of silicon oxide). To the silicasol, fine magnesium fluoride particles, an alumina sol, a titania sol ora zirconia sol may be added so that the refractive index of thetransparent coat layer can be controlled to change the reflectance ofthe transparent double-layer film.

In addition to the solvent and the noble-metal-coated fine silverparticles having an average particle diameter of from 1 nm to 100 nm,dispersed in the solvent, a silica sol as an inorganic binder componentelectro-constituting the binder matrix of the transparentelectro-conductive layer may also be mixed to make up the transparentelectro-conductive layer forming coating fluid. In such an instance,too, the transparent electro-conductive layer forming coating fluidcontaining the silica sol may be coated, optionally followed by drying,and thereafter the transparent coat layer forming coating fluid may beover-coated by the above coating process, thus a similar transparentdouble-layer film comprised of the transparent electro-conductive layerand the transparent coat layer can be obtained. For the same reasons asin the case of mixing the conductive fine oxide particles in thetransparent electro-conductive layer forming coating fluid, the silicasol to be mixed in the transparent electro-conductive layer formingcoating fluid may also preferably be desalted thoroughly beforehand.

As described above, according to the transparent electro-conductivestructure of the present invention, the transparent electro-conductivelayer of the transparent double-layer film constituted of thetransparent electro-conductive layer and transparent coat layer formedsuccessively on the transparent substrate is composed chiefly of i) thenoble-metal-coated fine silver particles having an average particlediameter of from 1 nm to 100 nm, the fine silver particles beingsurface-coated with the gold or platinum alone or composite of gold andplatinum, and ii) the binder matrix. Hence, compared with conventionaltransparent electro-conductive structures, it. has superior reflectionpreventive effect and transmission profile and also has a goodweatherability and a high electric-filed shielding effect.

Accordingly, the transparent electro-conductive structure can be used infront panels of display devices such as the CRTs previously stated,plasma display panels (PDPs), vacuum fluorescent display (VFD) devices,field emission display (FED) devices, electro-luminescence display (ELD)devices and liquid-crystal display (LCD) devices.

According to the transparent electro-conductive layer forming coatingfluid of the present invention, the coating fluid is composed chiefly ofthe solvent and the noble-metal-coated fine silver particles dispersedin the solvent and having an average particle diameter of from 1 nm to100 nm, the fine silver particles being surface-coated with the gold orplatinum alone or composite of gold and platinum. Hence, it caneffectively form a transparent double-layer film having a goodreflection preventive function and a good electric-filed shieldingfunction and also having a good transmission profile at the region ofvisible light rays and a good weatherability, compared with transparentelectro-conductive layers formed using conventional transparentelectro-conductive layer forming coating fluids.

Accordingly, the transparent electro-conductive structure usable infront panels of display devices such CRTs, PDPs and LCD devices can beobtained by forming the transparent electro-conductive layer by the useof this transparent electro-conductive layer forming coating fluid.

The present invention will be described below in greater detail bygiving Examples. The present invention is by no means limited to theseExamples. In the following, “%” refers to “% by weight” except for “%”of transmittance, reflectance and haze, and “part(s)” refers to “part(s)by weight”.

EXAMPLE 1

A colloidal dispersion of fine silver particles was made up by theCarey-Lea process. Stated specifically, to 33 g of an aqueous 9% silvernitrate solution, a mixed solution of 39 g of an aqueous 23% iron (II)sulfate solution and 48 g of an aqueous 37.5% sodium citrate solutionwas added, and thereafter the sediment formed was filtered and washed,followed by addition of pure water to make up a colloidal dispersion offine silver particles (Ag: 0.45%). To 15 g of this colloidal dispersionof fine silver particles, 0.5 g of an aqueous 1% hydrazine solution wasadded, and a mixed solution of 15 g of an aqueous potassium aurateRAu(OH₄) solution (Au: 0.1%) and 0.3 g of an aqueous 2% polymericdispersant solution was further added with stirring to obtain acolloidal dispersion of noble-metal-coated fine silver particles coatedwith gold alone. This colloidal dispersion of noble-metal-coated finesilver particles was desalted with an ion-exchange resin (available fromMitsubishi Chemical Industries Limited; trade name: DIAION SK1B,SA20AP), followed by ultrafiltration to obtain a concentrateddispersion. To this dispersion, ethanol (EA) and diacetone alcohol (DAA)were added to obtain a transparent electro-conductive layer formingcoating fluid containing noble-metal-coated fine silver particles (Ag:0.217%; Au: 0.057%; water: 11.8%; EA: 82.9%; DAA: 5.0%). The transparentelectro-conductive layer forming coating fluid thus obtained wasobserved on a transmission electron microscope to reveal that thenoble-metal-coated fine silver particles had an average particlediameter of 7.2 nm.

Next, the transparent electro-conductive layer forming coating fluidcontaining the noble-metal-coated fine silver particles was spin-coated(130 rpm, for 60 seconds) on a glass substrate (soda-lime glass of 3 mmthick) heated to 40° C., and thereafter subsequently a silica sol wasspin-coated thereon (130 rpm, for 60 seconds), followed by hardening at180° C. for 20 minutes to obtain a glass substrate provided with atransparent double-layer film constituted of a transparentelectro-conductive layer containing the noble-metal-coated fine silverparticles and a transparent coat layer formed of a silicate filmcomposed chiefly of silicon oxide, i.e., a transparentelectro-conductive structure according to Example 1.

Here, the above silica sol was made up using 19.6 parts ofMethyl-silicate 51 (trade name; available from Colcoat Co., Ltd.), 57.8parts of ethanol, 7.9 parts of an aqueous 1% nitric acid solution and14.7 parts of pure water to obtain one having SiO₂ (silicon oxide) solidcontent in a concentration of 10%, which was finally diluted with amixture of isopropyl alcohol (IPA) and n-butanol (NBA) (IPA/NBA=3/1) soas to have the SiO solid content in a concentration of 0.7%.

Film characteristics (surface resistance, visible light raytransmittance, standard deviation of transmittance, haze, and bottomreflectance/bottom wavelength) examined on the transparent double-layerfilm formed on the glass substrate are shown in Table 1 below. Thebottom reflectance is meant to be a minimum reflectance in thereflection profile of the transparent, electro-conductive structure, andthe bottom wavelength is a wavelength at the minimum reflectance. Thereflection profile of the transparent electro-conductive structureaccording to Example 1 is shown in FIGS. 1 and 3, and its transmissionprofile in FIGS. 2 and 4 together.

Transmittance shown in Table 1 in respect of only the transparentdouble-layer film, excluding the transparent substrate (glasssubstrate), at each wavelength plotted at intervals of 5 nm of awavelength region (380 to 780 nm) of visible light rays is determined inthe following way:

Transmittance (%) of only transparent double-layer film, excludingtransparent substrate (glass substrate)=[(transmittance measured on thewhole structure inclusive of transparent substrate)/(transmittance oftransparent substrate)]×100

Here, in the present specification, unless particularly noted, a valueobtained by measuring transmittance of the whole structure inclusive ofthe transparent substrate (i.e., the transparent substrate having thetransparent double-layer film, meant to be the transparentelectro-conductive structure) is used as the transmittance.

The surface resistance of the transparent double-layer film is measuredwith a surface resistance meter LORESTA AP (MCP-T400), manufactured byMitsubishi Chemical Industries Limited. The value of haze and thevisible light ray transmittance is measured with a haze meter (HR-200, areflectance-transmittance meter) manufactured by Murakami Color ResearchLaboratory, on the whole structure inclusive of the transparentsubstrate. The reflectance and the reflection and transmission profilesare measured with a spectrophotometer (U-400) manufactured by HitachiLtd. The particle diameter of the noble-metal-coated fine silverparticles is measured by observing the particles on a transmissionelectron microscope manufactured by Nippon Denshi K.K.

EXAMPLE 2

Using a colloidal dispersion of fine silver particles which was made upin the same manner as in Example 1, the procedure of Example 1 wasrepeated except that an aqueous 1.5% hydrazine solution and an aqueouspotassium aurate solution (Au: 0.15%) were used to obtain a transparentelectro-conductive layer forming coating fluid in whichnoble-metal-coated fine silver particles having an average particlediameter of 6.3 nm were dispersed (Ag: 0.221%; Au: 0.079%; water: 5.0%;EA: 89.7%; DAA: 5.0%) and the silica sol was diluted so as to have theSiO₂ (silicon oxide) solid content in a concentration of 0.65%. Thus, aglass substrate provided with a transparent double-layer filmconstituted of a transparent electro-conductive layer containing thenoble-metal-coated fine silver particles and a transparent coating layerformed of a silicate film composed chiefly of silicon oxide, i.e., atransparent electro-conductive structure according to Example 2, wasobtained.

Film characteristics examined on the transparent double-layer filmformed on the glass substrate are shown in Table 1 below. The reflectionprofile of the transparent electro-conductive structure according toExample 2 is shown in FIG. 5, and its transmission profile in FIG. 6.

EXAMPLE 3

Using a colloidal dispersion of fine silver particles which was made upin the same manner as in Example 1, the procedure of Example 1 wasrepeated except that an aqueous 0.5% hydrazine solution and an aqueouspotassium aurate solution (Au: 0.05%) were used to obtain a transparentelectro-conductive layer forming coating fluid in whichnoble-metal-coated fine silver particles having an average particlediameter of 6.8 nm were dispersed (Ag: 0.24%; Au: 0.028%; water: 3.7%;EA: 91.0%; DAA: 5.0%) and the silica sol was diluted so as to have theSiO₂ (silicon oxide) solid content in a concentration of 0.65%. Thus, aglass substrate provided with a transparent double-layer filmconstituted of a transparent electro-conductive layer containing thenoble-metal-coated fine silver particles and a transparent coating layerformed of a silicate film composed chiefly of silicon oxide, i.e., atransparent electro-conductive structure according to Example 3, wasobtained.

Film characteristics examined on the transparent double-layer filmformed on the glass substrate are shown in Table 1 below.

EXAMPLE 4

Using a colloidal dispersion of fine silver particles which was made upin the same manner as in Example 1, the procedure of Example 1 wasrepeated except that, without addition of the reducing agent aqueoushydrazine solution, 15 g of an aqueous potassium aurate solution (Au:0.05%) was added with stirring to effect displacement reaction betweengold and silver to obtain a colloidal dispersion of noble-metal-coatedfine silver particles and also obtain a transparent electro-conductivelayer forming coating fluid in which noble-metal-coated fine silverparticles having an average particle diameter of 6.5 nm were dispersed(Ag: 0.245%; Au: 0.025%; water: 7.6%; EA: 87.1%; DAA: 5.0%). Thus, aglass substrate provided with a transparent double-layer filmconstituted of a transparent electro-conductive layer containing thenoble-metal-coated fine silver particles and a transparent coating layerformed of a silicate film composed chiefly of silicon oxide, i.e., atransparent electro-conductive structure according to Example 4, wasobtained.

Film characteristics examined on the transparent double-layer filmformed on the glass substrate are shown in Table 1 below.

EXAMPLE 5

Using a colloidal dispersion of fine silver particles which was made upin the same manner as in Example 1, and using 0.4 g of an aqueous 1%hydrazine solution and an aqueous potassium aurate solution (Au:0.075%), a dispersion of noble-metal-coated fine silver particles havingan average particle diameter of 7.1 nm was obtained.

Then, the procedure of Example 1 was repeated except that an indium tinoxide (ITO) dispersion obtained by using fine ITO particles having anaverage particle diameter of 0.03 μm (available from Sumitomo MetalMining Co., Ltd.; trade name: SUFP-HX) and by desalting them thoroughlyby ion exchange was added in the above dispersion of noble-metal-coatedfine silver particles to finally obtain a transparent electro-conductivelayer forming coating fluid in which the noble-metal-coated fine silverparticles and the fine ITO particles were dispersed (Ag: 0.294%; Au:0.049%; ITO: 0.1%; water: 9.7%; EA: 84.95%; DAA: 4.9%), a silica solhaving a weight-average molecular weight of 1,920 was used and dilutedso as to have the SiO₂ (silicon oxide) solid content in a concentrationof 0.8%, a glass substrate heated to 35° C. was used and the transparentelectro-conductive layer forming coating fluid and the silica sol werespin-coated under conditions of 150 rpm for 60 seconds, followed byhardening at 210° C. for 20 minutes. Thus, a glass substrate providedwith a transparent double-layer film constituted of a transparentelectro-conductive layer containing the noble-metal-coated fine silverparticles and fine ITO particles and a transparent coating layer formedof a silicate film composed chiefly of silicon oxide, i.e., atransparent electro-conductive structure according to Example 5, wasobtained.

Film characteristics examined on the transparent double-layer filmformed on the glass substrate are shown in Table 1 below. The reflectionprofile of the transparent electro-conductive structure thus producedaccording to Example 5 is shown in FIG. 7, and its transmission profilein FIG. 8.

EXAMPLE 6

Using a colloidal dispersion of fine silver particles which was made upin the same manner as in Example 1, and using 0.4 g of an aqueous 1%hydrazine solution and an aqueous potassium aurate solution (Au:0.075%), a dispersion of noble-metal-coated fine silver particles havingan average particle diameter of 7.1 nm was obtained.

Then, the procedure of Example 1 was repeated except that an antimonytin oxide (ATO) dispersion obtained by using fine ATO particles havingan average particle diameter of 0.01 μm (available from Ishihara SangyoKaisha, Ltd.; trade name: SN-100P) and by desalting them thoroughly byion exchange was added in the above dispersion of noble-metal-coatedfine silver particles to finally obtain a transparent electro-conductivelayer forming coating fluid in which the noble-metal-coated fine silverparticles and the fine ATO particles were dispersed (Ag: 0.29%; Au:0.048%; ATO: 0.174%; water: 11.0%; EA: 83.58%; DAA: 4.9%), a silica solhaving a weight-average molecular weight of 1,920 was used and dilutedso as to have the SiO₂ (silicon oxide) solid content in a concentrationof 0.8%, a glass substrate heated to 35° C. was used and the transparentelectro-conductive layer forming coating fluid and the silica sol werespin-coated under conditions of 150 rpm for 60 seconds, followed byhardening at 210° C. for 20 minutes. Thus, a glass substrate providedwith a transparent double-layer film constituted of a transparentelectro-conductive layer containing the noble-metal-coated fine silverparticles and fine ATO particles and a transparent coating layer formedof a silicate film composed chiefly of silicon oxide, i.e., atransparent electro-conductive structure according to Example 6, wasobtained.

Film characteristics examined on the transparent double-layer filmformed on the glass substrate are shown in Table 1 below. The reflectionprofile of the transparent electro-conductive structure thus producedaccording to Example 6 is shown in FIG. 9, and its transmission profilein FIG. 10.

EXAMPLE 7

Using a colloidal dispersion of fine silver particles which was made upin the same manner as in Example 1, the procedure of Example 1 wasrepeated except that 0.4 g of an aqueous 1% hydrazine solution and anaqueous potassium aurate solution (Au: 0.075%) were used to obtain aconcentrated dispersion of noble-metal-coated fine silver particles, asolution containing a tetramer of tetramethyl-silicate (available fromColcoat Co., Ltd.; trade name: Methyl-silicate 51) as an inorganicbinder was added thereto to obtain a transparent electro-conductivelayer forming coating fluid in which noble-metal-coated fine silverparticles having an average particle diameter of 7.0 nm were dispersed(Ag: 0.29%; Au: 0.052%; SiO₂: 0.02%; water: 8.78%; EA: 85.85; DAA:5.0%), a silica sol having a weight-average molecular weight of 2,460was used and diluted so as to have the SiO₂ (silicon oxide) solidcontent in a concentration of 0.7%, a glass substrate heated to 35° C.was used and the transparent electro-conductive layer forming coatingfluid and the silica sol were spin-coated under conditions of 150 rpmfor 60 seconds, followed by hardening at 210° C. for 20 minutes. Thus, aglass substrate provided with a transparent double-layer filmconstituted of a transparent electro-conductive layer containing thenoble-metal-coated fine silver particles and a transparent coating layerformed of a silicate film composed chiefly of silicon oxide, i.e., atransparent electro-conductive structure according to Example 7, wasobtained.

Film characteristics examined on the transparent double-layer filmformed on the glass substrate are shown in Table 1 below.

EXAMPLE 8

To 33 g of an aqueous 9% silver nitrate solution, a mixed solution of 39g of an aqueous 23% iron (II) sulfate solution and 48 g of an aqueous37.5% sodium citrate solution was added, and thereafter the sedimentformed was filtered and washed, followed by addition of pure water tomake up a colloidal dispersion of fine silver particles (Ag: 0.49%). To240 g of this colloidal dispersion of fine silver particles, 5 g of anaqueous 1% hydrazine monohydrate N₂H₄.H₂O solution was added, and 200 gof an aqueous potassium platinate (IV) K₂Pt(OH₆) solution (Pt: 0.06%)was further added with stirring to obtain a colloidal dispersion ofnoble-metal-coated fine silver particles coated with platinum alone.This colloidal dispersion of noble-metal-coated fine silver particleswas subjected repeatedly to the step of concentrating it byultrafiltration, adding pure water to the resultant concentratedsolution and again concentrating it by ultrafiltration, to obtain adesalted concentrated dispersion. To this dispersion, ethanol (EA) anddiacetone alcohol (DAA) were added to obtain a transparentelectro-conductive layer forming coating fluid containingnoble-metal-coated fine silver particles (Ag: 0.245%; Pt: 0.025%; water:7.48%; EA: 87.25%; DAA: 5.0%). The transparent electro-conductive layerforming coating fluid thus obtained was observed on a transmissionelectron microscope to reveal that the noble-metal-coated fine silverparticles had an average particle diameter of 9.2 nm.

Next, this transparent electro-conductive layer forming coating fluidwas spin-coated (130 rpm, for 60 seconds) on a glass substrate(soda-lime glass of 3 mm thick) heated to 40° C., and thereaftersubsequently a silica sol was spin-coated thereon (130 rpm, for 60seconds), followed by hardening at 180° C. for 20 minutes to obtain aglass substrate provided with a transparent double-layer filmconstituted of a transparent electro-conductive layer containing thenoble-metal-coated fine silver particles and a transparent coating layerformed of a silicate film composed chiefly of silicon oxide, i.e., atransparent electro-conductive structure according to Example 8.

Here, the above silica sol was made up using 19.6 parts ofMethyl-silicate 51 (trade name; available from Colcoat Co., Ltd.), 57.8parts of ethanol, 7.9 parts of an aqueous 1% nitric acid solution and14.7 parts of pure water to obtain one having SiO₂ (silicon oxide) solidcontent in a concentration of 10%, which was finally diluted with amixture of isopropyl alcohol (IPA) and n-butanol (NBA) (IPA/NBA=3/1) soas to have the SiO₂ solid content in a concentration of 0.65%.

Film characteristics examined on the transparent double-layer filmformed on the glass substrate are shown in Table 1 below. The reflectionprofile of the transparent electro-conductive structure thus producedaccording to Example 8 is shown in FIGS. 11 and 13, and its transmissionprofile in FIGS. 12 and 14 together.

EXAMPLE 9

Using a colloidal dispersion of fine silver particles which was made upin the same manner as in Example 8, the procedure of Example 8 wasrepeated except that 6.3 g of an aqueous 1% hydrazine monohydrate N HH₂O solution and a mixed solution of 121 g of an aqueous potassiumaurate KAu(OH₄) solution (Au: 0.098%) and 121 g of an aqueous potassiumplatinate K₂Pt(OH₆) solution (Pt: 0.065%) were used to obtain atransparent electro-conductive layer forming coating fluid in whichnoble-metal-coated fine silver particles coated with a composite of goldand platinum and having an average particle diameter of 11.7 nm weredispersed (Ag: 0.26%; Au: 0.03%; Pt: 0.02%; water: 7.48%; EA: 87.2%;DAA: 5.0%). Thus, a glass substrate provided with a transparentdouble-layer film constituted of a transparent electro-conductive layercontaining the noble-metal-coated fine silver particles and atransparent coating layer formed of a silicate film composed chiefly ofsilicon oxide, i.e., a transparent electro-conductive structureaccording to Example 9, was obtained.

Film characteristics examined on the transparent double-layer filmformed on the glass substrate are shown in Table 1 below. The reflectionprofile of the transparent electro-conductive structure according toExample 9 is shown in FIG. 15, and its transmission profile in FIG. 16.

EXAMPLE 10

Using a colloidal dispersion of fine silver particles which was made upin the same manner as in Example 8, the procedure of Example 8 wasrepeated except that, without addition of the reducing agent aqueoushydrazine solution, 203 g of an aqueous potassium platinate K₂Pt(OH₆)solution (Pt: 0.064%) was added with stirring to effect displacementreaction between platinum and silver to obtain a transparentelectro-conductive layer forming coating fluid in which thenoble-metal-coated fine silver particles coated with platinum and havingan average particle diameter of 9.2 nm were dispersed (Ag: 0.24%; Pt:0.025%; water: 9.2%; EA: 85.53%, DAA: 5.0%). Thus, a glass substrateprovided with a transparent double-layer film constituted of atransparent electro-conductive layer containing the noble-metal-coatedfine silver particles and a transparent coating layer formed of asilicate film composed chiefly of silicon oxide, i.e., a transparentelectro-conductive structure according to Example 10, was obtained.

Film characteristics examined on the transparent double-layer filmformed on the glass substrate are shown in Table 1 below.

EXAMPLE 11

Using 240g of a colloidal dispersion of fine silver particles (Ag:0.49%) which was made up in the same manner as in Example 8, withoutaddition of the reducing agent aqueous hydrazine solution, 203 g of anaqueous potassium platinate K₂Pt(OH₆) solution (Pt: 0.064%) was addedwith stirring to effect displacement reaction between platinum andsilver to obtain a dispersion of noble-metal-coated fine silverparticles coated with platinum and having an average particle diameterof 9.2 nm.

Then, the procedure of Example 8 was repeated except that an indium tinoxide (ITO) dispersion obtained by using fine ITO particles having anaverage particle diameter of 0.03 μm (available from Sumitomo MetalMining Co., Ltd.; trade name: SUFP-HX) and by desalting them thoroughlyby ion exchange was added in the above dispersion of noble-metal-coatedfine silver particles to finally obtain a transparent electro-conductivelayer forming coating fluid in which the noble-metal-coated fine silverparticles and the fine ITO particles were dispersed (Ag: 0.312%; Pt:0.0325%; ITO: 0.12%; water: 12.3%; EA: 87.23%; DAA: 0%), a silica solhaving a weight-average molecular weight of 1,920 was used and dilutedso as to have the SiO₂ (silicon oxide) solid content in a concentrationof 0.8%, a glass substrate heated to 35° C. was used and the transparentelectro-conductive layer forming coating fluid and the silica sol werespin-coated under conditions of 150 rpm for 60 seconds, followed byhardening at 210° C. for 20 minutes. Thus, a glass substrate providedwith a transparent double-layer film constituted of a transparentelectro-conductive layer containing the noble-metal-coated fine silverparticles and fine ITO particles and a transparent coating layer formedof a silicate film composed chiefly of silicon oxide, i.e., atransparent electro-conductive structure according to Example 11, wasobtained.

Film characteristics examined on the transparent double-layer filmformed on the glass substrate are shown in Table 1 below. The reflectionprofile of the transparent electro-conductive structure according toExample 11 is shown in FIG. 17, and its transmission profile in FIG. 18.

COMPARATIVE EXAMPLE 1

Using a colloidal dispersion of fine silver particles which was made upin the same manner as in Example 1, the procedure of Example 1 wasrepeated except that the fine silver particles were not coated with goldto obtain a transparent electro-conductive layer forming coating fluidin which fine silver particles having an average particle diameter of6.9 nm were dispersed (Ag: 0.3%; water: 4.0%; EA: 90.7%; DAA: 5.0%).Thus, a glass substrate provided with a transparent double-layer filmconstituted of a transparent electro-conductive layer containing thefine silver particles and a transparent coating layer formed of asilicate film composed chiefly of silicon oxide, i.e., a transparentelectro-conductive structure according to Comparative Example 1, wasobtained.

Film characteristics examined on the transparent double-layer filmformed on the glass substrate are shown in Table 1 below. The reflectionprofile of the transparent electro-conductive structure according toComparative Example 1 is shown in FIGS. 1 and 11, and its transmissionprofile in FIGS. 2 and 12.

COMPARATIVE EXAMPLE 2

A transparent electro-conductive layer forming coating fluid prepared bydispersing in a solvent fine ITO particles having an average particlediameter of 30 nm (available from Sumitomo Metal Mining Co., Ltd.; tradename: SDA-104; ITO: 2%) was spin-coated (150 rpm, for 60 seconds) on aglass substrate (soda-lime glass of 3 mm thick) heated to 40° C., andthereafter subsequently a silica sol diluted so as to have SiO₂ (siliconoxide) solid content in a concentration of 1.0% was spin-coated thereon(150 rpm, for 60 seconds), followed by hardening at 180° C. for 30minutes to obtain a glass substrate provided with a transparentdouble-layer film constituted of a transparent electro-conductive layercontaining the fine ITO particles and a transparent coating layer formedof a silicate film composed chiefly of silicon oxide, i.e., atransparent electro-conductive structure according to ComparativeExample 2.

Film characteristics examined on the transparent double-layer filmformed on the glass substrate are shown in Table 1 below The reflectionprofile of the transparent electro-conductive structure according toComparative Example 2 is shown in FIGS. 1 and 11.

TABLE 1 *1 Noble Visible *2 metal Surface light ray Transmit- coatingresis- transmit tance Bottom reflectance/ Type of weight tance tancestandard Haze bottom wavelength fine particles (pbw) (Ω/□) (%) deviation(%) (%/nm) Example: 1 Ag—Au 26.0 490 72.7 3.29 0 0.1/515 2 Ag—Au 35.6390 69.4 2.00 0.1 0.05/495 3 Ag—Au 11.7 395 72.5 2.72 0.1 0.08/505 4Ag—Au 10.2 473 73.1 4.89 0 0.08/510 5 Ag—Au + ITO 16.7 456 74.8 3.01 0.40.46/540 6 Ag—Au + ATO 16.6 534 74.2 3.04 0.2 0.61/530 7 Ag—Au 17.9 31371.2 2.40 0 0.02/465 8 Ag—Pt 10.2 658 71.6 2.31 0 0.07/525 9 Ag—Au—Pt19.2 553 70.4 2.48 0.1 0.08/510 10  Ag—Pt 10.4 728 70.0 2.35 0.10.07/525 11  Ag—Pt + ITO 10.4 457 69.7 1.75 0.4 0.15/570 ComparativeExample: 1 Ag — 980 70.9 6.67 0.1 0.23/485 2 ITO — 16,000   93.3 — 0.20.83/540 pbw: parts by weight *1: Coating weight of the gold or platinumalone or composite of gold and platinum (noble metal) based on 100 partsby weight of silver. *2: Value with respect to the transmittance (%) ofonly the transparent double-layer film, excluding the transparentsubstrate, at each wavelength plotted at intervals of 5 nm of wavelengthregion (380 to 780 nm) of visible light rays.

Weatherability Test

The transparent electro-conductive structures according to Examples 1 to11 and the transparent electro-conductive structure according toComparative Example 1 were immersed in 5% brine to examine any changesof the surface resistance and film appearance of the transparentdouble-layer film provided on the transparent substrate (glasssubstrate) of each structure. The results are shown in Table 2 below.

TABLE 2 Surface resistance Initial value Appearance of double-layer film(Ω/□) Value after immersion in 5% brine (transmittance, haze,reflection) Example: 1 490 No change in surface resistance No changes intransmittance, haze and on immersion for 24 hr. reflection profile onimmersion for 24 hr. 2 390 No change in surface resistance No changes intransmittance, haze and on immersion for 24 hr. reflection profile onimmersion for 24 hr. 3 395 No change in surface resistance No changes intransmittance, haze and on immersion for 3 hr. Surface reflectionprofile on immersion for 1 hr. resistance changed to 3.1 kΩ/□ A slightchange in reflection color on on immersion for 24 hr. immersion for 24hr. 4 473 No change in surface resistance No changes in transmittance,haze and on immersion for 3 hr. Surface reflection profile on immersionfor 1 hr. resistance changed to 620 Ω/□ A slight change in reflectioncolor on on immersion for 24 hr. immersion for 24 hr. 5 456 No change insurface resistance No changes in transmittance, haze and on immersionfor 24 hr. reflection profile on immersion for 24 hr. 6 534 No change insurface resistance No changes in transmittance, haze and on immersionfor 24 hr. reflection profile on immersion for 24 hr. 7 313 No change insurface resistance No changes in transmittance, haze and on immersionfor 24 hr. reflection profile on immersion for 24 hr. 8 658 No change insurface resistance No changes in transrnittance, haze and on immersionfor 6 hr. Surface reflection profile on immersion for 6 hr. resistancechanged to 755 Ω/□ A slight change in reflection color on on immersionfor 24 hr. immersion for 24 hr. 9 553 No change in surface resistance Nochanges in transmittance, haze and on immersion for 24 hr. reflectionprofile on immersion for 24 hr. 10  728 No change in surface resistanceNo changes in transmittance, haze and on immersion for 6 hr. Surfacereflection profile on immersion for 6 hr. resistance changed to 1,031Ω/□ A slight change in reflection color on on immersion for 24 hr.immersion for 24 hr. 11  457 No change in surface resistance No changesin transmittance, haze and on immersion for 24 hr. reflection profile onimmersion for 24 hr. Comparative Example: 1 980 Surface resistancechanged to Haze increased on immersion for 30 min. >1,000,000 Ω/□ onimmersion for Transparent double-layer film peeled 15 min to becomeunmeasurable. partly on immersion for 10 hr.

Evaluation

(1) As can be seen from the results shown in Table 1, the values ofsurface resistance (Ω/□) and standard deviation of transmittance of thetransparent double-layer film according to each Example are confirmed tohave been greatly improved, compared with the values of the transparentdouble-layer film according to each Comparative Example. As also can beseen from the comparison of the transmission profiles of the transparentelectro-conductive structures according to Examples 1 and 8 with thetransmission profiles of the transparent electro-conductive structureaccording to Comparative Example 1 as shown in FIGS. 2 and 12, very flattransmission profiles are confirmed to be attained in the transparentelectro-conductive structures of Examples 1 and 8.

As can be seen from the reflection profiles shown in FIGS. 1 and 11, thetransparent electro-conductive structures of Examples 1 and 8 are alsoconfirmed to be improved also in reflection characteristics in thevisible light ray wavelength region, compared with those of ComparativeExamples 1 and 2.

(2) As can be seen from the results shown in Table 2, the transparentdouble-layer film according to each Example is confirmed to be greatlyimproved in weatherability, compared with the transparent double-layerfilm of Comparative Example 1.

(3) As can be confirmed from Table 1, in comparison of the visible lightray transmittance of the transparent electro-conductive structuresaccording to Examples 1 to 7, in which the noble-metal-coated finesilver particles coated with gold alone are used, the visible light raytransmittance of Examples 5 and 6, incorporated with ITO and ATO,respectively, shows higher values than that of other Examples.

On the other hand, as can be confirmed from Table 1, in comparison ofthe surface resistance of the transparent electro-conductive structuresaccording to Examples 8 to 11, in which the noble-metal-coated finesilver particles coated with gold or platinum alone or composite of goldand platinum are used, Example 11, incorporated with ITO, shows thesmallest value and also, in respect of the visible light raytransmittance, these Examples show substantially the same values. Thatis, this indicates that in Example 11 the transparent electro-conductivelayer can be made to have a higher visible light ray transmittance thanthat in Examples 8 to 10 when the transparent electro-conductive layeris made to have a thickness set smaller so as to have substantially thesame surface resistance as that in Examples 8 to 10.

From these facts, it is confirmed that an improvement of filmtransmittance in the transparent electro-conductive layer can beachieved when the conductive fine oxide particles of ITO or ATO areincorporated in the transparent electro-conductive layer.

(4) In Examples 1 to 11, the noble-metal-coated fine silver particlesare made using potassium aurate and potassium platinate as the aurateand platinate, respectively. In place of these potassium aurate andpotassium platinate, experiments have also been made using sodium aurateand sodium platinate.

The same evaluation tests as in Examples 1 to 11 have been made also inrespect of noble-metal-coated fine silver particles obtained using thesodium aurate and sodium platinate, and the same evaluation results asthose have been confirmed to be obtainable.

What is claimed is:
 1. A transparent electro-conductive layer formingcoating fluid used in the production of a transparent electro-conductivestructure having a transparent substrate and formed successively thereona transparent electro-conductive layer and a transparent coat layer;said coating fluid comprising a solvent and noble-metal-coated finesilver particles dispersed in the solvent and having an average particlediameter of from 1 nm to 100 nm, the fine silver particles beingsurface-coated with gold.
 2. The transparent electro-conductive layerforming coating fluid according to claim 1, wherein, in saidnoble-metal-coated fine silver particles, the gold is in a coatingweight set within the range of from 5 parts by weight to 100 parts byweight based on 100 parts by weight of silver.
 3. The transparentelectro-conductive layer forming coating fluid according to claim 1,which further comprises conductive fine oxide particles.
 4. Thetransparent electro-conductive layer forming coating fluid according toclaim 3, wherein said conductive fine oxide particles are fine particlesof a material selected from the group consisting of tin oxide, antimonytin oxide and indium tin oxide.
 5. The transparent electro-conductivelayer forming coating fluid according to claim 1 or 3, which furthercomprises an inorganic binder.
 6. A transparent electro-conductive layerforming coating fluid used in the production of a transparentelectro-conductive structure having a transparent substrate and formedsuccessively thereon a transparent electro-conductive layer and atransparent coat layer; said coating fluid comprising a solvent andnoble-metal-coated fine silver particles dispersed in the solvent andhaving an average particle diameter of from 1 nm to 100 nm, the finesilver particles being surface-coated with platinum alone or a compositeof gold and platinum.
 7. The transparent electro-conductive layerforming coating fluid according to claim 6, wherein, in saidnoble-metal-coated fine silver particles, the platinum alone orcomposite of gold and platinum is in a coating weight set within therange of from 5 parts by weight to 10) parts by weight based on 100parts by weight of silver.
 8. The transparent electro-conductive layerforming coating fluid according to claim 6, which further comprisesconductive fine oxide particles.
 9. The transparent electro-conductivelayer forming coating fluid according to claim 6, wherein saidconductive fine oxide particles are fine particles of a materialselected from the group consisting of tin oxide, antimony tin oxide andindium tin oxide.
 10. The transparent electro-conductive layer formingcoating fluid according to claim 6 or 8, which further comprises aninorganic binder.